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 $181.96   12.781%   $205.2163   $205.22   $205.20   $205.20  
  Purchase #2 $56.51   4.281%   $58.9292   $58.93   $58.95   $58.90  
  Purchase #3 $171.36   10.672%   $189.6475   $189.65   $189.65   $189.60  
  Purchase #4 $109.50   10.735%   $121.2548   $121.25   $121.25   $121.30  
  Purchase #5 $138.63   9.864%   $152.3045   $152.30   $152.30   $152.30  
  Purchase #6 $171.33   5.321%   $180.4465   $180.45   $180.45   $180.40  
  Purchase #7 $140.82   4.366%   $146.9682   $146.97   $146.95   $147.00  
  7 purchase totals = $970.11       $1,054.7670   $1,054.77   $1,054.75   $1,054.70