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 $61.48   13.289%   $69.6501   $69.65   $69.65   $69.70  
  Purchase #2 $88.56   3.572%   $91.7234   $91.72   $91.70   $91.70  
  Purchase #3 $236.66   3.605%   $245.1916   $245.19   $245.20   $245.20  
  Purchase #4 $31.31   12.288%   $35.1574   $35.16   $35.15   $35.20  
  Purchase #5 $19.96   10.385%   $22.0328   $22.03   $22.05   $22.00  
  Purchase #6 $135.73   8.871%   $147.7706   $147.77   $147.75   $147.80  
  Purchase #7 $230.43   6.115%   $244.5208   $244.52   $244.50   $244.50  
  7 purchase totals = $804.13       $856.0467   $856.04   $856.00   $856.10