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 $23.52   6.406%   $25.0267   $25.03   $25.05   $25.00  
  Purchase #2 $113.51   13.486%   $128.818   $128.82   $128.80   $128.80  
  Purchase #3 $166.78   13.776%   $189.7556   $189.76   $189.75   $189.80  
  Purchase #4 $179.28   4.839%   $187.9554   $187.96   $187.95   $188.00  
  Purchase #5 $213.62   10.470%   $235.986   $235.99   $236.00   $236.00  
  Purchase #6 $96.79   8.140%   $104.6687   $104.67   $104.65   $104.70  
  Purchase #7 $166.52   8.828%   $181.2204   $181.22   $181.20   $181.20  
  7 purchase totals = $960.02       $1,053.4308   $1,053.45   $1,053.40   $1,053.50