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 $65.58   4.740%   $68.6885   $68.69   $68.70   $68.70  
  Purchase #2 $249.73   10.170%   $275.1275   $275.13   $275.15   $275.10  
  Purchase #3 $104.51   4.194%   $108.8931   $108.89   $108.90   $108.90  
  Purchase #4 $132.93   13.434%   $150.7878   $150.79   $150.80   $150.80  
  Purchase #5 $233.39   4.152%   $243.0804   $243.08   $243.10   $243.10  
  Purchase #6 $192.52   6.232%   $204.5178   $204.52   $204.50   $204.50  
  Purchase #7 $160.65   10.156%   $176.9656   $176.97   $176.95   $177.00  
  7 purchase totals = $1,139.31       $1,228.0607   $1,228.07   $1,228.10   $1,228.10