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 $48.30   8.865%   $52.5818   $52.58   $52.60   $52.60  
  Purchase #2 $48.64   8.358%   $52.7053   $52.71   $52.70   $52.70  
  Purchase #3 $187.93   9.395%   $205.586   $205.59   $205.60   $205.60  
  Purchase #4 $120.76   10.280%   $133.1741   $133.17   $133.15   $133.20  
  Purchase #5 $240.92   13.222%   $272.7744   $272.77   $272.75   $272.80  
  Purchase #6 $204.79   7.505%   $220.1595   $220.16   $220.15   $220.20  
  Purchase #7 $63.59   11.674%   $71.0135   $71.01   $71.00   $71.00  
  7 purchase totals = $914.93       $1,007.9946   $1,007.99   $1,007.95   $1,008.10