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 $221.49   13.331%   $251.0168   $251.02   $251.00   $251.00  
  Purchase #2 $123.55   10.538%   $136.5697   $136.57   $136.55   $136.60  
  Purchase #3 $120.87   10.296%   $133.3148   $133.31   $133.30   $133.30  
  Purchase #4 $145.85   3.251%   $150.5916   $150.59   $150.60   $150.60  
  Purchase #5 $187.73   9.412%   $205.3991   $205.40   $205.40   $205.40  
  Purchase #6 $22.29   10.699%   $24.6748   $24.67   $24.65   $24.70  
  Purchase #7 $124.38   6.522%   $132.4921   $132.49   $132.50   $132.50  
  7 purchase totals = $946.16       $1,034.0589   $1,034.05   $1,034.00   $1,034.10