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 $52.77   10.413%   $58.2649   $58.26   $58.25   $58.30  
  Purchase #2 $231.54   9.635%   $253.8489   $253.85   $253.85   $253.80  
  Purchase #3 $121.96   8.695%   $132.5644   $132.56   $132.55   $132.60  
  Purchase #4 $216.98   9.643%   $237.9034   $237.90   $237.90   $237.90  
  Purchase #5 $184.58   13.786%   $210.0262   $210.03   $210.05   $210.00  
  Purchase #6 $196.43   3.360%   $203.03   $203.03   $203.05   $203.00  
  Purchase #7 $103.59   8.297%   $112.1849   $112.18   $112.20   $112.20  
  7 purchase totals = $1,107.85       $1,207.8227   $1,207.81   $1,207.85   $1,207.80