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 $210.31   8.669%   $228.5418   $228.54   $228.55   $228.50  
  Purchase #2 $62.26   11.573%   $69.4653   $69.47   $69.45   $69.50  
  Purchase #3 $36.38   5.163%   $38.2583   $38.26   $38.25   $38.30  
  Purchase #4 $64.82   5.715%   $68.5245   $68.52   $68.50   $68.50  
  Purchase #5 $219.84   6.158%   $233.3777   $233.38   $233.40   $233.40  
  Purchase #6 $235.66   11.241%   $262.1505   $262.15   $262.15   $262.20  
  Purchase #7 $222.99   8.237%   $241.3577   $241.36   $241.35   $241.40  
  7 purchase totals = $1,052.26       $1,141.6758   $1,141.68   $1,141.65   $1,141.80