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 $149.96   8.829%   $163.2   $163.20   $163.20   $163.20  
  Purchase #2 $243.39   13.215%   $275.554   $275.55   $275.55   $275.60  
  Purchase #3 $102.79   11.684%   $114.8   $114.80   $114.80   $114.80  
  Purchase #4 $250.67   11.277%   $278.9381   $278.94   $278.95   $278.90  
  Purchase #5 $25.84   12.410%   $29.0467   $29.05   $29.05   $29.00  
  Purchase #6 $93.81   9.187%   $102.4283   $102.43   $102.45   $102.40  
  Purchase #7 $204.43   12.280%   $229.534   $229.53   $229.55   $229.50  
  7 purchase totals = $1,070.89       $1,193.5011   $1,193.50   $1,193.55   $1,193.40