Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $175.99   10.570%   $194.5921   $194.59   $194.60   $194.60  
  Purchase #2 $181.48   13.638%   $206.2302   $206.23   $206.25   $206.20  
  Purchase #3 $188.65   11.838%   $210.9824   $210.98   $211.00   $211.00  
  Purchase #4 $61.82   6.504%   $65.8408   $65.84   $65.85   $65.80  
  Purchase #5 $193.50   9.668%   $212.2076   $212.21   $212.20   $212.20  
  Purchase #6 $241.49   6.519%   $257.2327   $257.23   $257.25   $257.20  
  Purchase #7 $219.51   12.402%   $246.7336   $246.73   $246.75   $246.70  
  7 purchase totals = $1,262.44       $1,393.8194   $1,393.81   $1,393.90   $1,393.70