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 $74.79   13.197%   $84.66   $84.66   $84.65   $84.70  
  Purchase #2 $167.33   5.597%   $176.6955   $176.70   $176.70   $176.70  
  Purchase #3 $77.95   5.720%   $82.4087   $82.41   $82.40   $82.40  
  Purchase #4 $198.77   3.133%   $204.9975   $205.00   $205.00   $205.00  
  Purchase #5 $228.28   13.311%   $258.6664   $258.67   $258.65   $258.70  
  Purchase #6 $184.70   13.355%   $209.3667   $209.37   $209.35   $209.40  
  Purchase #7 $62.31   5.436%   $65.6972   $65.70   $65.70   $65.70  
  7 purchase totals = $994.13       $1,082.4920   $1,082.51   $1,082.45   $1,082.60