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 $68.52   3.585%   $70.9764   $70.98   $71.00   $71.00  
  Purchase #2 $189.72   10.605%   $209.8398   $209.84   $209.85   $209.80  
  Purchase #3 $191.56   3.292%   $197.8662   $197.87   $197.85   $197.90  
  Purchase #4 $232.44   3.434%   $240.422   $240.42   $240.40   $240.40  
  Purchase #5 $197.46   8.660%   $214.56   $214.56   $214.55   $214.60  
  Purchase #6 $130.91   5.586%   $138.2226   $138.22   $138.20   $138.20  
  Purchase #7 $72.58   10.617%   $80.2858   $80.29   $80.30   $80.30  
  7 purchase totals = $1,083.19       $1,152.1728   $1,152.18   $1,152.15   $1,152.20