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 $121.88   8.311%   $132.0094   $132.01   $132.00   $132.00  
  Purchase #2 $140.87   4.236%   $146.8373   $146.84   $146.85   $146.80  
  Purchase #3 $113.56   3.467%   $117.4971   $117.50   $117.50   $117.50  
  Purchase #4 $204.49   3.247%   $211.1298   $211.13   $211.15   $211.10  
  Purchase #5 $75.77   8.825%   $82.4567   $82.46   $82.45   $82.50  
  Purchase #6 $104.38   3.614%   $108.1523   $108.15   $108.15   $108.20  
  Purchase #7 $210.74   8.444%   $228.5349   $228.53   $228.55   $228.50  
  7 purchase totals = $971.69       $1,026.6175   $1,026.62   $1,026.65   $1,026.60