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 $123.87   9.131%   $135.1806   $135.18   $135.20   $135.20  
  Purchase #2 $248.57   8.550%   $269.8227   $269.82   $269.80   $269.80  
  Purchase #3 $25.82   5.381%   $27.2094   $27.21   $27.20   $27.20  
  Purchase #4 $202.94   3.670%   $210.3879   $210.39   $210.40   $210.40  
  Purchase #5 $10.79   11.427%   $12.023   $12.02   $12.00   $12.00  
  Purchase #6 $185.96   4.436%   $194.2092   $194.21   $194.20   $194.20  
  Purchase #7 $176.31   10.767%   $195.2933   $195.29   $195.30   $195.30  
  7 purchase totals = $974.26       $1,044.1261   $1,044.12   $1,044.10   $1,044.10