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 $97.55   13.747%   $110.9602   $110.96   $110.95   $111.00  
  Purchase #2 $80.88   8.560%   $87.8033   $87.80   $87.80   $87.80  
  Purchase #3 $49.88   11.705%   $55.7185   $55.72   $55.70   $55.70  
  Purchase #4 $244.96   8.731%   $266.3475   $266.35   $266.35   $266.30  
  Purchase #5 $190.26   13.344%   $215.6483   $215.65   $215.65   $215.60  
  Purchase #6 $114.31   7.106%   $122.4329   $122.43   $122.45   $122.40  
  Purchase #7 $96.56   5.784%   $102.145   $102.15   $102.15   $102.10  
  7 purchase totals = $874.40       $961.0557   $961.06   $961.05   $960.90