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 $56.85   7.770%   $61.2672   $61.27   $61.25   $61.30  
  Purchase #2 $173.28   11.404%   $193.0409   $193.04   $193.05   $193.00  
  Purchase #3 $181.56   13.772%   $206.5644   $206.56   $206.55   $206.60  
  Purchase #4 $103.31   4.147%   $107.5943   $107.59   $107.60   $107.60  
  Purchase #5 $184.84   13.599%   $209.9764   $209.98   $210.00   $210.00  
  Purchase #6 $197.49   10.327%   $217.8848   $217.88   $217.90   $217.90  
  Purchase #7 $29.78   5.313%   $31.3622   $31.36   $31.35   $31.40  
  7 purchase totals = $927.11       $1,027.6902   $1,027.68   $1,027.70   $1,027.80