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 $37.34   11.107%   $41.4874   $41.49   $41.50   $41.50  
  Purchase #2 $180.39   11.793%   $201.6634   $201.66   $201.65   $201.70  
  Purchase #3 $177.46   7.804%   $191.309   $191.31   $191.30   $191.30  
  Purchase #4 $145.43   13.812%   $165.5168   $165.52   $165.50   $165.50  
  Purchase #5 $148.44   11.566%   $165.6086   $165.61   $165.60   $165.60  
  Purchase #6 $213.63   5.586%   $225.5634   $225.56   $225.55   $225.60  
  Purchase #7 $232.66   9.850%   $255.577   $255.58   $255.60   $255.60  
  7 purchase totals = $1,135.35       $1,246.7256   $1,246.73   $1,246.70   $1,246.80