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 $207.79   5.858%   $219.9623   $219.96   $219.95   $220.00  
  Purchase #2 $235.77   10.286%   $260.0213   $260.02   $260.00   $260.00  
  Purchase #3 $53.52   13.356%   $60.6681   $60.67   $60.65   $60.70  
  Purchase #4 $87.58   9.729%   $96.1007   $96.10   $96.10   $96.10  
  Purchase #5 $184.32   11.402%   $205.3362   $205.34   $205.35   $205.30  
  Purchase #6 $90.31   5.233%   $95.0359   $95.04   $95.05   $95.00  
  Purchase #7 $67.45   3.406%   $69.7473   $69.75   $69.75   $69.70  
  7 purchase totals = $926.74       $1,006.8718   $1,006.88   $1,006.85   $1,006.80