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 $48.81   7.642%   $52.5401   $52.54   $52.55   $52.50  
  Purchase #2 $153.94   11.629%   $171.8417   $171.84   $171.85   $171.80  
  Purchase #3 $209.52   13.494%   $237.7926   $237.79   $237.80   $237.80  
  Purchase #4 $85.41   6.538%   $90.9941   $90.99   $91.00   $91.00  
  Purchase #5 $212.43   11.228%   $236.2816   $236.28   $236.30   $236.30  
  Purchase #6 $201.84   4.231%   $210.3799   $210.38   $210.40   $210.40  
  Purchase #7 $172.89   10.642%   $191.289   $191.29   $191.30   $191.30  
  7 purchase totals = $1,084.84       $1,191.1190   $1,191.11   $1,191.20   $1,191.10