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 $238.77   11.298%   $265.7462   $265.75   $265.75   $265.70  
  Purchase #2 $71.74   12.431%   $80.658   $80.66   $80.65   $80.70  
  Purchase #3 $83.47   5.815%   $88.3238   $88.32   $88.30   $88.30  
  Purchase #4 $167.55   8.467%   $181.7365   $181.74   $181.75   $181.70  
  Purchase #5 $204.35   13.198%   $231.3201   $231.32   $231.30   $231.30  
  Purchase #6 $210.26   13.869%   $239.421   $239.42   $239.40   $239.40  
  Purchase #7 $13.32   7.393%   $14.3047   $14.30   $14.30   $14.30  
  7 purchase totals = $989.46       $1,101.5103   $1,101.51   $1,101.45   $1,101.40