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 $98.41   9.481%   $107.7403   $107.74   $107.75   $107.70  
  Purchase #2 $63.58   4.284%   $66.3038   $66.30   $66.30   $66.30  
  Purchase #3 $203.86   8.398%   $220.9802   $220.98   $221.00   $221.00  
  Purchase #4 $179.93   13.849%   $204.8485   $204.85   $204.85   $204.80  
  Purchase #5 $128.90   13.540%   $146.3531   $146.35   $146.35   $146.40  
  Purchase #6 $178.97   4.401%   $186.8465   $186.85   $186.85   $186.80  
  Purchase #7 $131.51   13.626%   $149.4296   $149.43   $149.45   $149.40  
  7 purchase totals = $985.16       $1,082.5020   $1,082.50   $1,082.55   $1,082.40