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 $159.72   9.628%   $175.0978   $175.10   $175.10   $175.10  
  Purchase #2 $105.27   4.517%   $110.025   $110.03   $110.05   $110.00  
  Purchase #3 $120.25   7.114%   $128.8046   $128.80   $128.80   $128.80  
  Purchase #4 $25.90   6.466%   $27.5747   $27.57   $27.55   $27.60  
  Purchase #5 $220.96   10.481%   $244.1188   $244.12   $244.10   $244.10  
  Purchase #6 $42.74   4.272%   $44.5659   $44.57   $44.55   $44.60  
  Purchase #7 $113.90   12.846%   $128.5316   $128.53   $128.55   $128.50  
  7 purchase totals = $788.74       $858.7184   $858.72   $858.70   $858.70