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 $142.61   7.728%   $153.6309   $153.63   $153.65   $153.60  
  Purchase #2 $45.88   8.166%   $49.6266   $49.63   $49.65   $49.60  
  Purchase #3 $145.82   4.481%   $152.3542   $152.35   $152.35   $152.40  
  Purchase #4 $243.30   3.284%   $251.29   $251.29   $251.30   $251.30  
  Purchase #5 $124.67   11.166%   $138.5907   $138.59   $138.60   $138.60  
  Purchase #6 $211.80   4.600%   $221.5428   $221.54   $221.55   $221.50  
  Purchase #7 $84.84   3.689%   $87.9697   $87.97   $87.95   $88.00  
  7 purchase totals = $998.92       $1,055.0049   $1,055.00   $1,055.05   $1,055.00